N323SR

On January 2, 2020, about 1015 eastern standard time, a Cirrus Design Corp. SR-22, N323SR, was substantially damaged when it was involved in an accident near Kenansville, North Carolina. The commercial pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that the departure and enroute phase of flight were normal for about 3.5 hours. While cruising at 6,500 ft mean sea level (msl), about 50 nautical miles from Curtis L Brown Jr. Field Airport (EYF), Elizabethtown, North Carolina, the airplane experienced three events nearly simultaneously. He first heard a “pop” that “wasn’t huge,” but caught his attention, then the autopilot disconnect aural alert sounded, and the airplane began “decelerating.” He stated that the airplane just began to “slow down” and the engine “wasn’t producing forward thrust.” However, the propeller continued to rotate, and when he viewed the engine instruments, the engine RPM continued to read 1,600 RPM, all exhaust gas temperature (EGT) gauges read 0° F, but no other engine instrument was red.

He reported that he adjusted the throttle lever after the loss of engine power; when it moved, the lever felt normal, but had no effect on the engine power. He also switched the fuel tank selector, but the engine condition did not change. He maintained 88 knots indicated airspeed as the airplane descended, and about 2,000 ft msl while approaching an open field ahead, he activated the Cirrus Airframe Parachute System (CAPS). Subsequently, the CAPS deployed and the airplane “stopped and fell near vertically.” The airplane impacted trees, where it became partially suspended in branches, with its right-wing impacting terrain below. The airplane’s fuselage and wings sustained substantial damage.

The National Transportation Safety Board (NTSB) Vehicle Recorders Division performed a download of the primary and multi-function displays. The data were largely consistent with what the pilot reported. The airplane’s flight and engine parameters were normal until a rapid drop in exhaust gas temperature (EGT) and oil pressure was observed in the final few minutes of data. Fuel flow remained consistent throughout the data, engine cylinder head temperatures were normal, and the engine rpm showed a slow decrease toward about 1,500 after the rapid drop in EGT was observed.

Examination of the engine revealed that it sustained minor impact damage. When the engine was rotated by hand, the No. 1 and 2-cylinder intake and exhaust valves moved normally, however, the remaining four cylinder’s valves displayed no movement. With the engine partially disassembled, the engine was rotated by hand and the camshaft gear was observed to rotate normally with no observable wear on any of its associated gear teeth. The engine was further disassembled and the camshaft was found fractured. The camshaft, part number 654084, revision P, was examined further by the NTSB Materials Laboratory.

According to the NTSB Materials Laboratory factual report, the camshaft had fractured between lobes associated with the No. 2 and 3 cylinders, intersecting oil transfer holes as shown in figure 1. The fracture plane was angled relative to the transverse plane consistent with fatigue fracture under torsion loading.

The fracture surface was further forensically examined, which revealed relatively smooth fracture features with curving crack arrest lines, features consistent with fatigue. Crack arrest lines emanated from origins at the corner of the oil transfer hole where it intersected the camshaft exterior surface. Fatigue features were observed around most of the fracture surface, intersecting the oil transfer hole at the opposite side of the camshaft. A portion of the fracture had post-fracture rub damage that obliterated the fracture features. The exterior surface of the camshaft had a dimpled appearance, consistent with a shot-peened surface treatment. The corner of the oil transfer hole was deformed inward, forming a burr. Dimple features were also observed on the surface of the burr consistent with peening deformation.

The oil transfer hole between lobes associated with the No. 4 and 5 cylinders also displayed a burr at the corner of the hole, but no crack was observed. Further forensic examination and cuts to the oil transfer hole found an elongated texture consistent with surface deformation associated with the burr formation.

Maintenance records revealed that the engine was newly manufactured by Continental on July 15, 2017, and was installed on the airplane by Cornerstone Aviation on August 5, 2017. The airplane was inspected under annual/100-hour and Cirrus Progressive inspection protocols from the engine install date, with the most recent inspection competed on September 22, 2019. Review of the maintenance endorsements from July 2017 through the most recent inspection revealed no work that would have involved major disassembly of the engine. The engine had accumulated a total of 707 hours.

Review of NTSB accident report ERA11LA130, January 27, 2011, involving a Cirrus SR22, Continental Motors IO-550-N, Camshaft Part Number 654084, revision D, revealed that the camshaft in that engine also fractured in-flight. The NTSB Materials Laboratory found that a fracture due to fatigue occurred at the most aft oil transfer hole. The report found that the engine had been overhauled about 393 hours prior to the incident. During the overhaul the original camshaft was replaced with a “repaired” camshaft and it was not determined whether any of the fatigue cracks were of detectible size at the time of installation.